Dual channel class-d amplifier

 

(57) Abstract:

Usage: in the amplifying devices and generator technology for broadband transmission paths of the audio frequency range. Dual channel class-D amplifier includes a two-rail pulse width modulator (1), two key amplifier (AFB) (2, 3), which outputs through the choke (4, 5) and transformers (7, 8) are connected in series and connected to the condenser (K) (6) of the filter. Additional To (9) provides a parallel connection of outputs KUM (2, 3) than is achieved by the implementation of strong ABD characterized by high efficiency and low distortion of the output signals. Effect: increase energy efficiency and reliability while improving the quality characteristics of the output signals of two-channel amplifier class d 3 Il.

The invention relates to the field of amplifier and generator technology and can be used in wideband transmission paths of the audio range of frequencies for broadcasting and zvukoprovodnost connection.

A well-known class D amplifiers [1, 2], which uses pulse-width modulation (PWM) and providing cost-effective utilinet amplifiers with PWM from the linear amplifiers from the energy point of view, especially when working on complex load. The power losses in the key amplifiers typically do not exceed 0.1 of the full output power PZ=UHIH, while for linear amplifiers, even in its most efficient mode In the relative losses reach values of 1.0-1.3 PZwith typical values of cosN= 0.1 to 0.3 (whereNis a phase shift between current and voltage;H= ZH/RH- the ratio of the active load resistance RHto the total impedance ZHfor parallel circuits).

To enhance the alternating low-frequency (LF) signals are known amplifiers with PWM mode class AD [1]. Known devices include pulse width modulator (PWM), key amplifier (AFB), made, for example, the half-bridge circuit, and a lowpass filter (LPF), performed on the inductor and the capacitor in parallel with the load.

The operating principle of amplifiers with PWM mode class AD is based on converting the amplified signal into a sequence of pulses modulated in duration, key strengthening capacity and demodulation LF components of the pulse voltage lower filter devices, located in the open or closed state. The main energy losses in the key elements associated with the change of their condition, the respective front or decay of the pulse modulated signal. Thus, the energy loss is almost proportional to the switching frequency (pulse frequency) and can be reduced with a corresponding reduction of the frequency modulated pulse sequence.

However, pulse modulation, key amplification and subsequent frequency signal demodulation in class D amplifiers, which leads to a significant Raman distortions. The components of the Raman frequencieskn= k-n(- frequency switching, the frequency of the amplified signal) penetrate the bandwidth of LPF, which significantly degrades the quality characteristics of known devices. A characteristic feature of the amplifiers with PWM mode of AD is the formation and strengthening of the se pulse sequence, close to meander at low levels of the amplified low-frequency signal. While the components of the switching frequency after low-pass filter with a frequency traceC= 0,2 reach significant levels (up to minus 30 dB from the maximum Mthe amplitude of the LF signal), which limits Dean is a nominal voltage UH=0,7 UMup to 20-30% when UH=0,1 UM.

When working on a complex load, such as paths zvukoprovodnost connection, the ratio of the upper frequencyBthe amplified signal to the cutoff frequency ofCLPF equalB/C= 0.5, it is essential to ensure the stability of the amplitude-frequency and phase-frequency characteristics of the output voltage of an amplifying device. The characteristics of the quality of the output signal can be improved by improving relations /Bup to 15-20. For the upper frequency B= 15 kHz this condition is possible with a = 200-300 kHz. The implementation of key power amplifiers based on the advanced element base for such switching frequencies leads to an energy loss of less than 0.2 PZthat corresponds to the efficiency of amplification devices are not more than 80%.

Known methods of increasing the efficiency of key amplifiers with PWM based on the use mode BD [1, 3]. Such a mode is possible in the key amplifiers (AFB), made by bridge circuits in the management of amplifying devices from the push-pull pulse width Converter. In amplifiers with PWM mode BD dynamic energy losses can be reduced by the second circuit. When changing the polarity of the half wave of the signal amplification provided by the other diagonal of the bridge circuit.

The presence of a phase shift between the output voltage and current KUM leads to a significant non-linear distortion of the output signal due to interruption of current inductor low-pass filter. Known technical solutions [3], allowing to reduce these distortions due to the switching of the diagonals of the bridge circuit when the change of the output current. However, in a bridge circuit KUM mode BD are characteristic distortion at low signal levels, similar distortions in linear amplifiers-class Century For key amp distortion of this type is due to delays3the inclusion of key elements, relative3which size /2 reaches 3-5% at a frequency switching f = /2100 kHz.

The introduction of such delays is a necessary condition for the elimination of through currents through the key elements and accordingly reliable operation of the amplifying device. In turn, the presence of delays at low output currents leads to breakage of the output current of the inductor and distortion of the amplitude characteristics. Kind of distortion in this zone has the shape of a step, the relative amount which dostet small input signals and can be defined as the zone of silence". When the input signal in this zone, the voltage at the output of the amplifier is missing, which limits the dynamic range of such a device at the level of 20-30 dB. The distortions of the amplitude characteristic causes harmonic distortion of the output voltage, the value of which increases from 2-3% to 30% when changing the output voltage from 0 dB to -20 dB. Thus, a decrease in Raman distortion in the amplifier mode BD when compared with AD is associated with increasing harmonic distortion and limit the dynamic range of the amplification.

Closest to the proposed is a two-channel amplifier with PWM mode AD, described in the copyright certificate 1438583 [4]. The device prototype is performed according to certain rules on the vapor sawtooth generator (STG), two Comparators connected in the circuit a vapor-phase pulse-width Converter, two key power amplifiers, two chokes and filter capacitor, and outputs vapor sawtooth generator is connected with the first inputs of the respective Comparators, the second inputs of which are connected with the bus of the input signal, and outputs connected to the inputs of the key is cut corresponding inductors connected to the filter capacitor and the output signals of the device.

The structural scheme of the device of the prototype is shown in Fig.2, contains a two-rail SPIKE 1, including STG 1.1, Comparators 1.2, 1.3, and key amplifiers 2, 3, chokes 4, 5, condenser 6. Key power amplifier device of the prototype can be made by well-known scheme of U.S. patent 4115740 on half-bridge circuits are connected in parallel by the bus power to the tires of the primary voltage. Each half-bridge circuit is performed on the two key elements with turn-on delay required for their reliable operation.

Two-channel amplifier operates as follows. GPN 1.1 generates two sawtooth mutually opposite phase voltage UP1UP2received at the first inputs of the Comparators 1.2, 1.3, on a second input which receives an input signal U. the result of comparing the input signal with a sawtooth voltage generated two sequences of pulses modulated in duration, which are amplified by the power allocated to the outputs KUM 2, 3 in the form of a pulse voltage V1V2:

V1=E sign[U(t)-UP1(t)],

V2=E sign[U(t)-UP2(t)].

The pulse voltage V1V2are fed to the inputs of the respective dresses is determined by the relative amplitude of the input signal m=UM/UPM, the supply voltage E and the load impedance ZN:

ILF=Eat/ZN.

The maximum amplitude of the RF current IVCMoccurs when the minimum input signal and is defined by the expression

IVCM=E/4fL,

where L is the inductance of the inductor 4, 5.

High-frequency components of the current of the inductors 4, 5 at low signal levels mutually opposite phase, thus achieving a significant reduction of high-frequency components of the output voltage generated at the capacitor 6 of the filter. The specified advantage distinguishes the device is a prototype from the well-known single-channel amplifiers with PWM mode AD.

However, in two-channel amplifier with PWM retains the advantages of AD, namely the presence of RF current at small signal levels provides linearity amplitude and minimizing harmonic distortion small output voltages at the level of 2-3%. In turn compensated HF components of the current individual channels are achieved small ripple of the output voltage and the expansion of the dynamic range up to 40-50 dB.

Along with selected advantages with single-channel PWM for each channel of the amplifier is filtered to separate low-pass filter. This required that the frequency ratioB,Cnecessary for the implementation of the key amplifying device, especially when working on complex load:

/C10;C/B2.

Accordingly, the frequency of switching in the channels of amplification to the upper frequency of the amplified signal must be at least 20. Noted condition leads to the necessity of increasing the switching frequency and, consequently, to increase the dynamic energy losses and, accordingly, decrease the efficiency of the device.

Additionally, the parallel addition of the output signals of the amplification channels implemented in the device prototype leads to the imbalance of the output currents of the key power amplifiers. As key elements have very small own residual voltage V0/E=0,01-0,03, even a minor imbalance in the duration of pulse processes, such as 2-4%, leads to a significant imbalance low output currents of more than 20-50%. The presence of such imbalance leads to different current loading of the key elements of QOM and, as consequence, to decrease in the reliability of their work.

Thus, the device prototype is characterized SS="ptx2">

The present invention is to increase energy efficiency and reliability while improving the quality characteristics of the output signals of the dual-key amplifier class d

To solve the problem in known two-channel class-D amplifier containing two-rail pulse width modulator, an input connected to the input bus of the device, and outputs to the corresponding inputs of the two key power amps, made in half-bridge circuits, bus power supply are connected in parallel and connected to the tires of positive and negative voltages, the key outputs of the amplifiers are connected in parallel through the first and second inductors connected to the capacitor and the output bus device, additionally introduced two transformers and an additional capacitor, moreover, the findings of the first and second inductors is disconnected from the capacitor and connected to the first findings of the primary windings of the respective transformers, the latter findings are connected to a common bus supply, in turn secondary windings of the transformers are connected in series and connected between the terminals of the capacitor and the output chinatechnical result from the use of the proposed solutions is to increase energy efficiency and reliability through the implementation of the mode class ABD sequential addition of the output signals of the key channels of amplification. In the inventive device eliminates the unbalance currents channel gain, realized the advantages of dual channel PWM, allowing the lowering of the switching frequency while improving the quality characteristics of the output signals.

A structural scheme of the device and timing diagrams of signals explaining his work, is shown in Fig.1 and Fig.3. The structural scheme of the device of the prototype is shown in Fig.2.

The proposed device (Fig.1) contains a two-rail SPIKE 1, two key amplifier GODFATHER 2, GODFATHER 3, the chokes 4, 5, condenser 6, and two transformers 7, 8 and the additional capacitor 9. Blocks of the proposed technical solutions are performed according to certain rules, the key amplifiers can be implemented in accordance with U.S. patent 4115740.

The work of the proposed dual-key class-D amplifier is as follows.

To paraphase the DOWEL 1 in the comparison with the opposite phase of the sawtooth voltage UP1UP2the amplified signal U is converted to two sequences of pulse width modulated pulses which are fed to the control inputs KUM 2, 3. As a result, the output of Clitellata:

V1=E sign[U(t)-[UP1(t)],

V2=E sign[U(t)-UP2(t)].

The pulse voltage V1V2through the respective inductors 4, 5 and transformers 7, 8 are formed in series and are connected to the output capacitor 6 and the output bus device. This addition is equivalent to the connection of the total voltage V via a low-pass filter of the second order LfWITHfto the load. For transformation coefficient KTthe total voltage V, is given to the secondary windings, as well:

V=KT(V1+V2).

The parameters of the lowpass filter in the load circuit is determined by the inductance L of the choke 4, 5 and the capacity of the capacitor 6:

Lf=2LT2WITHf=S.

It should be noted that the inclusion of an additional capacitor 9 has virtually no effect on the characteristics of the output filter on the useful frequency components of the amplified signal. This circumstance is explained by the fact that the LF components of the voltages V1V2defined the amplified signal in phase and equal in amplitude. Therefore, through the condenser 9 LF components of the current practically does not close.

In turn, when TLD and switching frequency, in the spectra of the pulse voltage V1and V2mutually opposite phase. Accordingly, the capacitor 9 provides a flow of high frequency current through the key elements KUM 2 and 3, including at low modulation levels (at low levels of the amplified signal). At high levels, modulation of the high frequency component of the output current is significantly reduced.

Thus, in the proposed device, at low levels of the amplified signal current closed alternately through the key elements similar to AD, and at high levels is achieved by sequential addition of the pulse voltages is similar to mode BD. This mode can be defined as the mode class ABD characterized by improved power characteristics and indicators of the quality of the output signals. The advantage of the mode class ABD implemented in the proposed device is sequential addition of pulse voltages, which allows full use of the advantages of dual channel PWM. The rate of change of the total pulse signal exceeds twice the switching frequency of the individual channels of amplification with two times greater relative level of useful bass sostav the who solution allows almost 1.5-2 times to reduce the switching frequency in the key channels of amplification, which results in a corresponding reduction of the dynamic energy losses. The presence of high frequency components of the current through the key elements at low levels of the amplified signal, due to the inclusion of additional capacitor 9, eliminates distortion amplitude characteristics and the provision of small distortions in the expansion of the dynamic range of the amplified signals.

Thus, in the proposed two-channel class-D amplifier enable additional capacitor and transformer provides a promising mode of class ABD sequential addition of signals with dual PWM. Series connection of the channels AFB provides equality LF output current, which distinguishes the proposed device provides improved reliability in comparison with a device prototype. Non-identity of the maximum amplitudes of the output current of QOM in the device prototype reaches 50-70%, and in the proposed device does not exceed 10% of the stock is achieved using the key elements of the current and, therefore, increase the reliability of their functioning.

Implementation of the regime of ABD provides the possibility of lowering the switching frequency of the disorder, provided by the introduction of new elements and relationships, reaches solving the problem of the invention.

So, if you know of an amplifying device of the class D in the frequency range of the amplified signal of 20 kHz has an efficiency of no more than 80-85% with non-linear distortions of more than 3% and a dynamic range of less than 40 dB, the proposed device provides an efficiency of about 90-93%, harmonic distortion less than 1% and a dynamic range in excess of 50 dB. Experimental studies have confirmed the advantages of the claimed technical solution that allows you to recommend the proposed device to the introduction of transmission paths broadcasting and zvukoprovodnost connection.

Literature

1. Artem A. D. class D Amplifiers and key generators in radio communications and broadcasting. M: Communications, 1980, S. 207.

2. Kibaki C. M. fundamentals of the key methods of strengthening. M: Energy, 1980, S. 232.

3. Alexanian, A. A. , Galakhov Century A. Distortion in push-pull amplifiers low frequency PWM. Radio engineering, 1986, 10.

4. A. C. 1438583, a Key regulator. N 03 TO 7/02. Publ. 30.12.1990.

Dual channel class-D amplifier containing two-rail pulse width modulator, an input connected to the input bus stroitelnogo and negative voltage supply, inputs connected to respective outputs of the two-rail pulse-width Converter, and the outputs are connected with the first pins of the first and second inductors, respectively, and the first capacitor, connected to the first and second pins to the output bus device, characterized in that the input of the second capacitor and two transformers, and the second terminals of the inductors is connected to the first findings of the primary windings of the respective transformers, the latter findings are connected to a common bus supply, and the secondary windings of the transformers are connected in series and connected between the first and second findings of the first capacitor, and the second capacitor included the first and second pins between the second terminals of the inductors.

 

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